Gonorrhea is a sexually transmitted disease (STD) caused by the human pathogen, Neisseria gonorrhoeae (gonococcus), a Gram-negative, intracellular, aerobic diplococcus that can grow and rapidly multiply in the mucous membranes. Gonococcal infection remains a major global health problem with more than sixty million cases reported annually worldwide (A. C. Gerbase et al., Lancet, 1998, 351 (Suppl. 3): 2-4). According to the Centers for Disease Control and Prevention (CDC), gonorrhea is the second most frequently reported STD in the United States with almost 400,000 new cases reported each year (CDC, “Summary of Notifiable Disease—United States. 2001”, Morb. Mortal. Wkly Rep., 2001, 50:1-108; CDC, “Sexually Transmitted Disease Surveillance, 2001”, U.S. Department of Health and Human Services, Atlanta, Ga., 2002; CDC, “Sexually Transmitted Disease Surveillance, 2002”, U.S. Department of Health and Human Services, Atlanta, Ga., 2003). Like chlamydia, the most prevalent bacterial STD in the U.S., gonorrhea is substantially under-reported, and approximately twice as many new infections are estimated to occur each year as are reported (H. Weinstock et al., Persp. Sex. Reprod. Health, 2004, 36: 6-10). Under-reporting is substantial, at least in part, because gonorrhea is asymptomatic in 30-60% of infected women and up to 10% of infected men. Unrecognized and untreated, Neisseria gonorrhoeae may remain infectious in the host for several months, which may facilitate its spread and promote a reservoir of infection.
When they are present, initial symptoms of gonococcal infection in women include dysuria, vaginal discharge, vaginal bleeding between periods, and abdominal pain. Left untreated, women with gonorrhea are at risk of developing serious complications from the infection, regardless of the presence or severity of symptoms. In particular, gonorrhea can lead to a severe, painful pelvic infection with inflammation of the fallopian tubes and ovaries called pelvic inflammatory disease (PID) (E. W. Hook III and H. H. Handsfield, in “Sexually Transmitted Diseases”, K. K. Holmes et al. (Eds.), 3rd Ed., 1999, pp. 451-466, McGraw-Hill: New York, N.Y.). PID can cause permanent damage to the fallopian tubes, uterus, and surrounding tissues, which can lead to chronic pelvic pain, infertility, and potentially fatal ectopic pregnancy (W. Cates Jr. et al., Am. J. Obstet. Gynecol., 1991, 164: 1771-1781; J. Coste et al., Fertil. Steril., 1994, 62: 289-295; L. Weström and P. Wolner-Hansen, Genitourin. Med., 1993, 69: 9-17). In men, the most common initial symptoms are dysuria and purulent discharge from the urethra. The average incubation for gonorrhea is approximately 2 to 5 days following sexual contact with an infected partner; however, symptoms may appear as late as 30 days. Neisseria gonorrhoeae may spread from the urethra to other portions of the male reproductive tract causing epididymitis, prostatitis, and various other conditions such as periurethral abscess. Untreated gonorrhea may lead to urethral stricture, which can result in decreased urine flow, incomplete emptying of the bladder, urinary tract infection, and ultimately kidney failure. Rarely (in 1-3% of infected women and a lower percentage of infected men), the bacterium disseminates via the blood causing arthritis, bacteremia or endocarditis (E. W. Hook III and H. H. Handsfield, in “Sexually Transmitted Diseases”, K. K. Holmes et al. (Eds.), 3rd Ed., 1999, pp. 451-466, McGraw-Hill: New York, N.Y.). Although gonorrhea is known primarily as a sexually transmitted infection, it can also be transmitted to the newborn during delivery through an infected birth canal. This can cause blindness, joint infection or a life-threatening blood infection to the baby.
Although patients with any sexually transmitted disease are at increased risk of co-infection with another STD, co-infection of chlamydia and gonorrhea is most common (up to 40% of women and up to 20% of men with gonorrhea are also infected with chlamydia). Epidemiologic and biologic studies provide strong evidence that gonococcal infections increase susceptibility to and facilitate transmission of human immunodeficiency virus (HIV) in both men and women (M. S. Cohen et al., Lancet, 1997, 349: 1868-1873; D. T. Fleming and J. N. Wasserheit, Sex. Transm. Infect., 1999, 75: 3-17; K. A. Workowski and W. C. Levine, Morb. Mortal. Wkly Rep., 2002, 51 (RR06): 1-80; T. A. Farley et al., J. Acquir. Immun. Defic. Syndr., 2003, 33: 642-648).
Early detection is an essential component of public health programs to control gonococcal infection. The goals of early detection and early treatment include interruption of the chain of transmission, prevention of long-term sequelae, and reduction of duration of infectiousness to limit the risk of co-infection. Early detection may also prevent over-treatment, which is a major concern due to widespread N. gonorrhoeae antibiotic resistance (CDC, “Fluoroquinolone-resistance in Neisseria gonorrhoeae, Hawaii, 1999, and decreased susceptibility to azithromycin in N. gonorrhoeae, Missouri, 1999”, Morb. Mortal. Wkly Rep., 2000, 49: 833-837; CDC, “Increases in fluoroquinolone-resistant Neisseria gonorrhoeae—Hawaii and California, 2001”, Morb. Mortal. Wkly Rep., 2002, 51: 1041-1044; CDC, “Increases in fluoroquinolone-resistant Neisseria gonorrhoeae among men who have sex with men—United States, 2003, and revised recommendations for gonorrhea treatment, 2004”, Morb. Mortal. Wkly Rep., 2004, 53: 335-338).
Isolation of Neisseria gonorrhoeae in cell culture has been the traditional method for laboratory diagnosis and has remained the method of choice for medico-legal specimens because of its specificity. However, this method requires stringent transport conditions to preserve specimen viability and has a turnaround time of 2 to 3 days. In many settings, cell culture has been replaced by more rapid tests based on antigen detection by direct fluorescent antibody staining, enzyme immunoassays, and enzyme-linked immunosorbent assays (ELISA), which have less demanding transport requirements and can provide results on the same day. However, these methods are still laborious and time-consuming and, more importantly, lack sensitivity as screening assays, especially for asymptomatic patients.
More recently, nucleic acid-based hybridization probe tests have been developed for direct detection of Neisseria gonorrhoeae. These tests offer higher specificity but no substantial improvement on sensitivity. Furthermore, most of these tests are performed on endocervical or urethral specimens, which are obtained using invasive sampling procedures. Nucleic acid amplification assays based on polymerase chain reaction (PCR), ligase chain reaction (LCR), strand-displacement amplification (SDA), or transcription-mediated amplification (TMA) technology are now available. In addition to offering all the advantages of non-culture tests in terms of ambient specimen transport, batching automation, and rapid processing time, these assays provide higher specificity and a sensitivity approaching 100%. Furthermore, they can be performed on less invasive clinical specimens such as urine. All these advantages make nucleic acid amplification assays particularly suited for detection of asymptomatic gonococcal infection and as a screening tool.
However, existing nucleic acid amplification assays for gonorrhea detection still exhibit certain disadvantages and limitations. The primary concerns involve false-negative results caused by the presence of amplification inhibitors in certain specimens and false-positive results due to cross-contamination if strict quality control procedures are not applied. Clearly, the development of improved nucleic acid amplification assays for the detection of gonococcal infection remains highly desirable.